When a strip of sheet such as of paper or plastic is wound up in a fixed width by a winding machine, the sheet is generally wound up while the opposite lateral edges of the sheet are cut off as with slitters. In the cutting unit of the winding machine, therefore, narrow strips of waste sheet of irregular width are discharged in a large volume. Since these strips of scrap sheet generally have small width, it has been customary for such strips to be wound up on a winding frame as swung laterally as though they were wire ropes being wound on a winding barrel. In that case, a drive mechanism for the winding frame is set so that the winding frame will be rotated at a speed slightly higher than the speed at which the strips of scrap sheet are discharged, and the excess rotation of the winding frame is absorbed by means of a slip mechanism annexed to the drive mechanism for the winding frame. As a result, proper tension is imparted at all times to the cut strips of scrap sheet which are being wound up.
The winding torque of the winding frame not only generates winding tension but also imparts driving tension to the cut strips of scrap sheet being discharged from the cutting unit of the sheet winding machine. Since the cut strips of scrap sheet, while being wound up, are subject to the inertia such as of the the winding frame provided with a flange and the rolls of the cut strips of scrap sheet being wound up, however, the winding torque cannot promptly respond to variation which may occur in the discharging speed of the cut strips of scrap sheet. Consequently, there ensues the possibility that the cut strips of scrap sheet may break under heavy tension and that the wound rolls may slacken. Further, since the strips of scrap sheet are wound up directly into rolls without being held down to a suitable level by touch rollers, the volume of air entrapped between successive plies of strip of sheet in the rolls can not be controlled. If the volume of air entrapped between successive plies increases in certain portions of such plies, or if the thickness of the strip of scrap sheet varies, even slightly, in certain portions in the length of the sheet, the rolls on the winding frame are finished with an outwardly curved surface, an inwardly curved surface, or an irregularly rising and falling surface. The rolls thus obtained, therefore, are not uniform in diameter in the direction of the axis of the winding frame. Even when the winding torque of the winding frame is retained at a fixed magnitude, such nonuniform diameters of the rolls bring about variation in the driving tension of the strips of scrap sheet and may cause the rolls to slacken or the strips in motion to break.
Particularly, in recent years, the winding of sheet is performed at a high speed, and the sheet winding machine is abruptly started at a high speed and abruptly decelerated. The conventional scrap winding machine used for winding cut strips of scrap sheet, therefore, fails at times to wind the strips by keeping pace with the motion of the scrap of sheet discharged from the sheet winding machine. Thus, there ensues the possibility that the strips of scrap sheet so discharged will break or slacken en route to the rolls growing in diameter on the winding frame and that the broken ends or slackened portions will entangle themselves in the sheet winding machine, making it inevitable to stop not only the scrap winding machine but also the sheet winding machine operated for commercial production.